High capacity travelling wave tube for amplifying ultra high frequencies



HIGH CAPACITY TRAVELLING WAVE TUBE FOR July 30, 1963 'w. VEITH ETAL3,099,766

AMPLIFYING ULTRA HIGH FREQUENCIES- Filed Oct. 30, 1961 10 'III II 1 r(1,1

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3,699,766 Patented July 30, 1963 fire 3,tl99,766 HIGH CAPACHY TRAVELLENGWAVE TUBE FGR AMPLIFYENG ULTRA HIGH FREQUENCIES Werner Veith and PaulMeyerer, Munich, Germany, as-

Signors to Siemens & Halslre Aktiengesellschaft, Berlin and Munich, acorporation of Germany Filed Oct. 30, 1961, Ser. No. 148,656 Claimspriority, application Germany Nov. 2, 1964) 9 Claims. (Cl. 315-35) Thisinvention is concerned with a high capacity travelling wave tube,especially for the amplification of ultra high frequencies, employingpurely electrostatic focusing of the electron beam, wherein the electronbeam which is guided about the tube axis along a spiral path interactswith an electromagnetic Wave which is propagated along this spiral path.

There is already known a travelling wave tube wherein the electrons arepropagated upon helical paths along a helical delay line surrounding apreferably cylindrical cathode. The corresponding tube is constructed inthe manner of a magnetic field tube. Accordingly, for guiding orfocusing the electron beam, there is required a magnetic fieldcooperating with additional electric fields.

There is also known a travelling wave tube with purely electrostaticfocusing in which the electron beam is upon an orbital path guidedthrough the radial field of a cylinder condenser, one electrode of whichis constructed as a delay line, so that an electromagnetic wave canazimuthally spread upon such electrode. The delay effected by this lineis in accordance with the supposition customary for travelling wavetubes so selected that the phase angle velocity of the electromagneticWave is approximately equal to the angular velocity of the electrons.The orbital path of the electron beam is stabilized by the equilibriumobtaining between the force, acting due to the electrostatic field ofthe cylinder condenser, and the centrifugal force of the electrons. Theconsiderable advantage of this known travelling wave tube resides inthat no magnetic field is required for the guidance of the electronbeam. However, the power of this tube is relatively low due to thelimited length of the orbital path.

The object of the invention is to provide a high capacity travellingwave tube with purely electrostatic focusing.

It might be feasible to realize this object by modifying the aboveindicated known travelling Wave tube with purely electrostatic focusingin accordance with the previously indicated magnetic field tube.Accordingly, the electron beam would in such tube run upon a spiral pathbetween an inner conductor and a delay line surrounding the innerconductor along the spiral path of the electron beam, whereby the innerconductor would have to be connected with a high positive voltage.

However, it was found that such a tube would have a number of drawbacks:Maximum coupling between the electron beam and the delay line would befrom the outset impossible since an electron beam running along a spiralpath has the greatest density interiorly, that is, upon the side facingaway from the delay line; moreover, the electrons move increasingly awayfrom the delay line due to yielding energy to the high frequency fieldof the line, thereby further reducing the coupling between the electronbeam and the delay line. The coupling between the electron beam and thedelay line would also be aifected by the fact that the delay line Wouldnot have a closed or continuous surface, such as the outer electrode ofa cylinder condenser, but would be formed, due to the periodicstructure, by individual rods or webs. To the electron beam would beimparted an angular path, instead of a circular path, so that theelectrons would be in the region of the interaction areas lying betweenthe rods or webs, farther away from the delay line than they would 2 bein the case of an ideal cylinder condenser. In order to obtain asatisfactory coupling, it would be necessary to guide the electron beamso close along the delay line that the release of secondary electronswould be unavoidable. The released secondary electrons would impact thepositively biased inner electrode with high velocity, thereby causing animpermissible heating of the tube.

It is, therefore, for the solution of the problems underlying theobjects of the present invention, in connection with a high capacity orhigh power travelling wave tube, especially for amplifying highestfrequencies, with purely electrostatic focusing of the electron beam,wherein the electron beam, which is guided about the tube axis upon aspiral path interacts with an electromagnetic wave propagated along thispath, in accordance with the invention proposed, to guide the electronbeam within a spirally wound hollow delay line or wave guide structurewith periodic openings of at least the wall parts thereof facing thetube axis, in the space between a metallic element (outer electrode)arranged within and electrically separated from the delay line structureand the wall parts thereof lying toward the tube axis (inner electrode)which are connected with a direct positive potential.

The advantage of the travelling wave tube according to the inventionresides in that the high frequency energy is despite the absence of amagnetic field, similarly as in a magnetron, not derived from thekinetic energy of the electrons but from the potential energy of theelectrostatic field. An electron moving in the space between the outerelectrode and the inner electrode would be subjected to braking forcesupon giving off kinetic energy for conversion into high frequencyenergy. Since the electron loses thereby centrifugal force, it willreach a path nearer to the inner electrode, which extends upon apotential plane of a higher potential than that of the original path.The electron accordingly retains the same angular velocity, so that thesynchronism is preserved which exists between the electrons of theelectron beam and an elec tromagnetic wave propagated along the delayline. The electrons thereby move ever closer to the inner electrode,whereby the coupling between the electron beam and the high frequencyfield of the delay line is further improved.

In order to avoid, in a travelling wave tube according to the invention,undue disturbance of the high frequency properties of the delay line, itis advantageous to construct the outer electrode so that it comes in theregion of the webs between which extends the high frequency field,closer to the inner electrode than in the range of the interaction areasbetween the webs. Such construction of the outer electrode also has theadvantage that the electron beam is guided particularly close to theinner electrode in the regions of the interaction areas.

The efficiency of a travelling wave tube according to the invention canbe increased, based upon an interaction mechanism which is similar tothat of a magnetron, by constructing the collector for the electron beamof electrically mutually separated parts, and by connecting to theindividual parts a direct potential of such magnitude that therespective impact energy of the electrons becomes as low as possible.The par-ts of the collector which are subjected to the impact ofelectrons extending along a lower potential plane are for this purposeplaced on a direct po tential which is correspondingly lower than thatconnected to the parts which are subjected to the impact of electronsextending along higher potential planes.

Further features and details of the invention shall now be explainedwith reference to the schematic figures shown in the accompanyingdrawing in which parts not absolutely necessary for an understanding ofthe invention have been omitted. Corresponding parts are identicallyreferenced in the various figures.

FIG. 1 represents a cross-sectional view of a cylinder condenser;

FIG. 2 shows the amplifier part of a travelling wave tube formed by sucha cylinder condenser, wherein the inner electrode is formed by webs of adelay line structure;

FIG. 3 indicates a structure having a polygonal outer electrode;

FIG. 4 shows an outer electrode of another configuration;

FIG. 5 illustrates a portion of an example of an embodiment of atravelling .wave tube according to the invention; and

FIG. 6 shows in sectional view the collector end of a travelling wavetube according to the invention, having a particularly advantageouscollector for the electron beam.

Referring now to FIG. 1, showing in cross-sectional representation acylinder condenser, numeral 1 indicates the outer electrode and numeral2 the inner electrode. The amplifier part of a travelling wave tubeaccording to the invention forms approximately such a cylindercondenser, whereby the inner electrode 2 is however formed by parts of adelay line structure represented as webs or rods 3 (-FIG. 2) betweenwhich extends the high frequency field of the line. The remaining partsof the de.ay line structure, which are to be enveloped by the outerelectrode 1, have been omitted from the drawing. To the rods 3 is, ascompared with the outer electrode 1, connected a high direct potential,resulting in an electrostatic field indicated in FIG. 3 by the arrows 4.Within the space between the outer electrode l and the rods 3 is guidedan electron beam upon the path 5, such beam being guided in stablemanner due to the fact that the force acting as a result of theelectrostatic field is in equilibrium with the outwardly directedcentrifugal force of the electrons. The path '5 is not circular as inthe case of an ideal cylinder condenser, but angular. The angular formhas, as compared with the circular form, the advantage that theelectrons come closer to the interaction paths lying bet-ween the rods 3than they come to the rods. The coupling between the electron beam andthe high frequency field, which is already relatively good owing to thegreater density interiorly of the electron beam, is thereby improved.

The angular path of the electrons can be emphasized by appropriateconfiguration of the outer electrode, such that the outer electrodecomes in the region of the rods or webs 3 closer to the inner electrodethan in the regions of the interaction areas extending between the rods3. Such configuration also avoids detrimentally affecting the delay lineby the outer electrode. A suitable embodiment of a polygonal outerelectrode is shown in FIG. 3 and another embodiment thereof is shown inFIG. 4.

Such an outer electrode can be produced in particularly simple manner bydrilling holes in an originally circular structure at points lyingopposite the interaction areas. In FIGS. 3 and 4, the bars 3 areangularly formed in the direction of the outer electrode so as to obtainin the regions of the bars a stronger concentration of the electrostaticfield.

FIG. 5 shows a partial view of m embodiment of a travelling wave tubeaccording to the invention. The hollow delay line or wave guidestructure 6, the inner wall of which is broken in meandering manner, iswound spirally. The tongue or finger-like wall parts 7 remaining betweenthe meandering open portions correspond to the rods or bars 3 in FIGS. 2to 4. interiorly of the structure 6 is disposed 21 Likewise spirallywound metal member 8 which is electrically separated from the structure6. The metal member 8 may be held by means of a member 9 which is sealedby fusing in the outer wall of the structure '6 and which shall alsoserve as a terminal. The metal member 8 is placed on cathode potentialreferred to a voltage of 0 volt or less, and the structure '6 disposedopposite thereto is placed on a high direct voltage. The electron beam10 is thereby in stable manner guided upon l its path between the metalstructure 8 and the webs 7.

Decisive for the interaction mechanism of the tube is only the periodicstructure of the delay line as such, and it should therefore suffice toarrange a delay line with periodic structure only upon the inside of theelectron beam 163'. However, it was found that such a delay line cannotbe advantageously dimensioned. Accordingly, in a travelling wave tubeaccording to the invention, the main mass of the delay line structure isalways disposed on the outside. The outer wall of the delay hasstructure 6 therefore can advantageously form the outer wall of thetube.

The arrangement of the main mass of the delay line on the outsidenecessarily results in loading of the outer electrode, such loading inturn resulting in a shifting of the conduction character toward longerwaves. Accordingly, the geometrical dimensions of the delay linestructure can thereby be held smaller than in the case of a line withoutloading, whereby the geometrical dimensioning of the tube is furtherfacilitated.

The advantage of the construction of the outer electrode 8 in the mannerillustrated in FIG. 5, namely, with radially inwardly directed band-likeextensions 11 and 12 respectively at the upper and the lower marginthereof, resides in that it prevents an intertwined how of the electronbeam longitudinally of the tube. The band-like extensions 11 and 12accordingly function in the manner of auxiliary focusing electrodes.

A delay line according to FIG. 5 is in simple manner constructed from ahollow cylindrical copper block. Such block is machined so that thereremains interiorly of the wall a fiat band-shaped spindle correspondingto the horizontal parts of the delay line structure 6. Into the freeledge of the spindle are milled an odd number of grooves which aresymmetrically distributed over the circumference thereof. Into thesegrooves are soldered webs at the center thereof, after inserting theouter elctrode into the line. The length of the webs exceeds the pitchof the spindle, so that the ends of the webs interlace interdigitally inthe direction of the spindle.

A delay line structure according to FIG. 5 has a rearwardly runningfundamental wave. For amplifier operation, the tube must therefore bedimensioned so that the electron beam is in synchronism with the firstforwardly running partial wave. This results in the advantage that thedispersion of the forwardly running first partial wave is in theillustrated delay line structure very slight.

FIG. 6 shows a sectional view of the collector end of a travelling wavetube provided with a particularly advantageous collector. Owing to theinteraction with the high frequency field of the delay line, theelectrons of the electron beam move at the end of the tube along pathsof different radii. The electrons with the greatest energy loss followthe smallest radius, therefore moving closely interiorly at the innerwall of the delay line structure 6.

The electrons with the least energy loss move outside at the outerelectrode ll. The collector is therefore subdivided into three annularmetal members 13, 14, 15. These metal members are electrically mutuallyseparated and connected to different potentials. The rnetal member 13with the smallest diameter receives the highest positive directpotential and the metal member 15 with the greatest diameter receivesthe lowest positive direct potential. This arrangement makes it possibleto keep the respective impact energy of the electrons low.

The invention is not inherently limited to the illustrated and describedembodiments. It is in particular possible to use in place of the delayline according to FIG. 5 another suitable periodic structure.

Changes may be made within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

We claim:

1. A high capacity travelling wave tube, especially for amplifying ultrahigh frequencies, with purely electrostatic focusing of the electronbeam, wherein the electron beam which is guided about the tube axis upona helical path, enters into reciprocal action with an electromagneticwave propagated along such path, said wave spreading with azimuthaldelay upon a helically extending hollow delay line structure providedwith periodic breaks formed at least in the wall parts thereof facingthe tube axis, in the space between a metallic structure, forming anouter electrode, the latter and the delay line extending helically inmutually parallel relation about the tube axis with the outer electrodeelectrically separated from the delay line structure and wall parts ofthe delay line structure, forming an inner electrode, said delay lineforming a part of a hollow cylindrical metal structure which, jointlywith the delay line structure, surrounds the outer electrode.

2. A travelling wave tube according to claim 1, wherein said outerelectrode is constructed so that parts thereof come closer to the innerelectrode in the area of webs disposed between said periodic breaks thanthey come at the areas of said breaks.

3. A travelling wave tube according to claim 2 wherein said outerelectrode is cross-sectionally polygonal.

4. A travelling wave tube according to claim 2, wherein said outerelectrode has circular recesses formed therein at the areas of saidbreaks.

5. A travelling wave tube according to claim 2, wherein said webs areangularly shaped at the parts thereof which face said outer electrode.

6. A travelling wave tube according to claim 1, wherein said outerelectrode is at its respective upper and lower margin provided with aradially inwardly directed extension for limiting the electrode beamlongitudinally of the tube aXis'.

7. A travelling wave tube according to claim 6, wherein said delay linestructure comprises a generally rectangular shaped wave guide, the wallof said Wave guide facing the tube axis being broken meander-like, saidouter conductor being held in said wave guide in insulated relation withrespect to the delay line structure.

8. A travelling wave tube according to claim 1, having a collector forthe electron beam comprising a plurality of annular electricallyseparated metallic members of different diameter, the respective membersof smaller diameter being placed on a higher positive direct potentialthan the respective neighboring metal member of smaller diameter.

9. A travelling wave tube according to claim 8, wherein said collectorcomprises three successively stage-like positioned annular metalmembers.

References Cited in the file of this patent UNITED STATES PATENTS2,325,865 Litton Aug. 3, 1943 2,730,678 Dohler et al Jan. 10, 19562,844,797 Dench July 22, 1958 2,900,558 Watkins Aug. 18, =-9

3,058,025 Hogg Oct. 9, 1962 FOREIGN PATENTS 1,006,335 France Jan. 23,1952

1. A HIGH CAPACITY TRAVELLING WAVE TUBE, ESPECIALLY FOR AMPLIFYING ULTRAHIGH FREQUENCIES, WITH PURELY ELECTROSTATIC FOCUSING OF THE ELECTRONBEAM, WHEREIN THE ELECTRON BEAM WHICH IS GUIDED ABOUT THE TUBE AXIS UPONA HELICAL PATH, ENTERS INTO RECIPROCAL ACTION WITH AN ELECTROMAGNETICWAVE PROPAGATED ALONG SUCH PATH, SAID WAVE SPREADING WITH AZIMUTHALDELAY UPON A HELICALLY EXTENDING HOLLOW DELAY LINE STRUCTURE PROVIDEDWITH PERIODIC BREAKS FORMED AT LEAST IN THE WALL PARTS THEREOF FACINGTHE TUBE AXIS, IN THE SPACE BETWEEN A METALLIC STRUCTURE, FORMING ANOUTER ELECTRODE, THE LATTER AND THE DELAY LINE EXTENDING HELICALLY INMUTUALLY PARALLEL RELATION ABOUT THE TUBE AXIS WITH THE OUTER ELECTRODEELECTRICALLY SEPARATED FROM THE DELAY LINE STRUCTURE AND WALL PARTS OFTHE DELAY LINE STRUCTURE, FORMING AN INNER ELECTRODE, SAID DELAY LINEFORMING A PART OF A HOLLOW CYLINDRICAL METAL STRUCTURE WHICH, JOINTLYWITH THE DELAY LINE STRUCTURE, SURROUNDS THE OUTER ELECTRODE.